Most applications requiring high forces, such as robotic arms and lifts, use hydraulic actuators to develop the required force to move a payload. A hydraulic actuator system requires a gas or electric motor driven pump, a reservoir, fluid lines and control valves operated either by hand or a microprocessor. It would be desirable to replace the hydraulic actuators and the ancillary components required to operate them in these applications with lightweight, high force electro-mechanical actuators.
Hydraulic actuators provide a mechanical advantage not unlike a gearbox or a transmission. With hydraulic pump and actuator systems the force multiplication or mechanical advantage is simply the ratio of the area of the pump piston(s) to the area of the actuator piston. A hydraulic actuator is synonymous with a simple motor and gearbox since each produces a mechanical advantage. Therefore, electric motor gearbox systems have been used to attempt to replace hydraulic actuators. Although high forces can be produced using an electric motor and gearbox this comes at a sacrifice in output speed, which is proportional to the gearing ratio. The solution for increasing the response time is not simply a matter of speeding up the motor feeding the gearbox since the torque the motor produces typically reduces as speed is increased. Therefore, to increase response time the motor must not only run at a higher speed, but must also increase in size. This increase in size not only adds to system weight, but typically exceeds the allowable footprint area for the actuator system.
Most linear and rotary actuators have an angular displacement as stator and armature poles come into and out of alignment. This angular displacement results in forces acting upon two axes. One axis represents the force acting in the direction of the motion and the other axis represents the attractive force that attempts to pull the moving pole and the stationary pole together, which is perpendicular to the direction of motion. The useable force to perform work is the vector sum of these forces. It would be desirable to provide techniques for improved utilization of axial forces.